1. Field of the Invention
The present invention relates to an organic electroluminescent device, particularly to an organic electroluminescent device which can completely separate its components from external conditions without using a cap and clearly reduce its thickness without installing a getter.
2. Description of the Prior Art
Organic electroluminescence is the phenomenon that excitons are formed in an (low molecular or high molecular) organic material thin film by re-combining holes injected through an anode with electrons injected through a cathode, and light of specific wavelength is generated by energy from thus formed excitons.
Organic electroluminescent device using the above phenomenon has a basic structure as illustrated in FIG. 1. The basic structure of organic electroluminescent device includes a glass substrate 1, an indium-tin-oxide layer 2 (hereinafter, referred as “ITO layer”) acting as anode electrode, formed on the upper side of the glass substrate 1, and an insulating layer, an organic material layer 3, and a metal layer 4 acting as cathode electrode in order.
For reference, the organic material layer 3 has the structure that a hole injection layer for injecting holes into the device; a hole transport layer for transporting the holes injected from the anode electrode to a light emitting layer; the light emitting layer which electron supplied from the cathode electrode and holes supplied from the anode electrode are recombined and light is emitted therefrom; and an electron transport layer for transporting electron supplied from the cathode electrode are stacked in order.
The organic electroluminescent device having the above structure is manufactured through the following processes. First, the ITO layer 2 is deposited on the glass substrate 1 through the vacuum deposition method, and the ITO layer 2 is patterned by the photolithography method.
Then, an insulating layer (not shown), the organic material layer 3, and walls W are formed on the patterned ITO layer 2. The organic material layer 3 is formed on the insulating layer, and the metal layer 4 acting as the cathode is formed on the organic material layer 3. Here, each wall W is formed to separately deposit the metal layers 4 on the ITO layer 2.
After each component is formed as described above, a cap 6 is bonded on a periphery portion of the substrate 1 by a sealant 5. As shown in FIG. 1, a closed space is formed between the cap 6 and the substrate 1, and so the above components disposed in this space are not influenced by external conditions such as moisture and the like.
Here, organic material constituting the device is vulnerable to moisture and heat, and thus the cap 6 used for protecting the components from external conditions is made from metal, glass, or synthetic material thereof. Also, an ultraviolet ray-curable adhesive is used as the sealant 5.
On the other hand, a getter 8 which is moisture absorbent is attached to a lower surface of the central portion of the cap 6 by a tape 7 made from organic material. Moisture (humidity) remains in the space between the cap 6 and the substrate 1 at which the structural components constituting the device are disposed. Therefore, in order to absorb the moisture, the getter 8 is attached to a lower surface of the cap 6, and then the cap 6 is bonded to the substrate 1.
The getter 8 used for the above-explained purpose is made from, for example, calcium oxide (CaO), barium oxide (BaO), etc., and can be applied in the form of film, paste, or powder.
The organic electroluminescent device shown in FIG. 1 needs a space for the getter 8. Also, the metal layer 4 is oxidized in case the getter 8 and the metal layer 4 are contacted with each other, and so a certain space is needed between the metal layer 4 and the getter 8. This structure acts as a factor increasing thickness of the device. Thus, it is desirable to eliminate the factor increasing thickness of the device in order to conform to the trend of miniaturization of the device itself and apparatus that the device is mounted to.